Electric control circuits



April 30, 1963 E. G. ANGER ELECTRIC CONTROL CIRCUITS Original Filed Oct.1, 1957 REGULATED 2 DC souwcz TIME RATE CONTRO LLE R SPEED REGUL ATlNGCONTROLLER FIG. 1

INVENTOR.

ERNEST G. ANGER M I United States Patent 3,088,064 ELECTRIC CONTROLCIRCUITS Ernest G. Anger, Wauwatosa, Wis., assignor to Square D Company,Detroit, Mich, a corporation of Michigan Continuation of applicationSer. No. 687,533, Oct. 1, 1957 This application June 6, 1960, Ser. No.34,198 7 Claims. (Cl. 320-4) This invention relates to electric controlcircuits and more particularly to a transistorized circuit which willdelay the response of a control circuit and is a continuation ofapplication Serial No. 687,553, filed October 1, 1957, now abandoned.

The present invention is directed to a transistorized time delay circuitwhich will delay the immediate response of a DC. motor controller tochanges in the speed setting of the controller. While various systemssuch as disclosed in Patent No. 2,902,634 or in Patent No. 2,786,975,which has been assigned to the assignee of the present invention, haveproved satisfactory in use, the transistorized circuit according to thepresent invention will provide an improved time rate delay with fewercomponents than the circuits heretofore known. More particularly, thecircuit according to the present invention will operate on low voltagesand with this low voltage will provide an almost perfect time rate delayfor the motor speed controller. Further, the transistors which are usedin the time rate delay circuit will not only operate efficiently withthe low voltages but will function as diodes to freely pass current inone direction with a minimum voltage drop and will act as currentamplifiers when controlling current flow in the opposite direction. Thisresult is not possible with any of the time rate delay circuits nowknown.

It is an object therefore of the present invention to provide anefiicient time rate delay circuit for a DC. motor speed controller whichwill operate on relatively low voltages and will amplify the changes inspeed settings for the motor.

A further object of the present invention is to utilize a transistorizedtime rate delay circuit which will retard the response of a DC. motorcontroller during both acceleration and deceleration of the motor.

Another object of the present invention is to control the charging anddischarging of a capacitor which is connected to delay the response of aDC. motor controller with a circuit which will charge the capacitor by aconstant current at a substantially low voltage irrespective of thevariations in the charging voltage.

A further object of the present invention is to supply the emitters of apair of transistors in a time rate delay circuit with substantiallyconstant current from a simple low voltage floating source and tocontrol the emitter current with smaller signal currents so as toutilize the transistors as diodes and current amplifiers in the circuit.

Further objects and features of the invention will be readily apparentto those skilled in the art from the specification and appended drawingsillustrating a preferred embodiment in which:

FIG. 1 shows schematically a DC motor speed controller as utilizing thetime rate delay device according to the present invention.

FIG. 2 shows a circuit diagram of a time rate delay device according tothe present invention as used in the circuit in FIG. 1.

In the drawings, and in FIG. 1 particularly, a control system forregulating the speed of a motor 10 is shown wherein the motor 16 isenergized by a D0. generator 12. which is rotated by a suitable devicesuch as an AC. motor, not shown. The excitation of the generator field14 is controlled by a speed regulating controller 16 to control theoutput of the generator 12 and thereby control the speed of the motor 10in the conventional manner.

The present invention is directed to a time rate device 20 forcontrolling the acceleration and deceleration of the motor 10 and asshown is connected between an output slider 22 of the speed settingpotentiometer and a pair of input leads 24 and 26 to the controller 16.A voltage signal is supplied from the time rate controller 20 over leads24 to 26 to the speed regulating controller 16. The motor also suppliesthe speed regulating controller 16 with a voltage signal proportional tothe motor speed. The speed regulating controller algebraically adds thevoltage signals and uses the resultant thereof to control the generatorfield 14. In normal continuous operation, that is, when the motor 10 isoperating at a speed determined by the setting of the slider 22 on thepotentiometer, the time rate delay device 20 furnishes a throughconnection with minimum possible voltage drop and operates as a closedswitch contact so the regulated motor speed will properly respond to thesetting of the slider 22 on the potentiometer. When the setting of theslider 22 is suddenly moved to increase or decrease the speed of themotor 10, or the contacts of the starting switch are actuated to startthe motor, the device 20 will provide the controller 16 with a signalchanging at a controlled rate until the speed of the motor correspondsto the setting of the slider 22.

Typical time rate acceleration controllers are usually arranged toprovide adjustable acceleration and deceleration delays which areadjustable to vary the change over intervals which vary from 2 to 20seconds. It is to be appreciated that one of the requirements of a timerate device is that its timing must be linear and provide a constantrate of change in motor speed over the preselected time interval settingof the device. A device which will accomplish this result is shown inFIG. 2 of the drawings. Before a discussion of the operation of thecircuit in FIG. 2 is undertaken, it is believed that a discussion ofsome of the characteristics of the transistors utilized in the circuitmay be of aid in understanding the operation and advantages of thecircuits shown. It is well known that a transistor is a constant currentconducting device and may be connected to act as a common base connectedamplifier wherein the input signal is intro duced into the emitter-basecircuit and the output signal is extracted from the collectonbasecircuit and the base electrode is common to the input and outputcircuit. That is, for constant transistor emitter currents, when thebase is controlling the conduction of current through the collector, thecollector will have a substantially constant output current regardlessof the collector to base voltage. Another characteristic of a transistoris that when the voltage bias between the collector and base becomes avalue slightly less than zero, the transistor will become sharplynon-conductive. Further reversal of the bias between the collector andbase will cause the transistor to conduct strongly as a diode in thereverse direction. Another feature of interest in the transistors usedis that they will act as amplifiers. That is, a small change in theemitter to base current will result in a large change in collectorcurrent flow.

Considering the circuit shown in FIG. 2 of the drawings, a battery 30, avoltage regulating tube 32, a fixed resistance 34 and three variablepotentiometer resistances 36, 38, and 40 comprise the DC. regulatedvoltage source corresponding to the potentiometer in FIG. 1 wherein thevariable tap 42 on potentiometer 38 is analogous to the slider 22. It isclearly apparent the battery 30, which represents a DO source, may bereplaced by an A.C. transformer and bridge type rectifier combinationwith suitable filter networks to provide a DC. voltage between leads 44and 46 which voltage is made constant by the glow tube 32 which is aregulating tube and connected to provide a constant voltage betweenjunction 48 and lead 46. The potentiometers 36 and 40 are included torespectively adjust the maximum and minimum speeds of motor 10.

The circuit shown in FIG. 2 includes a capacitor 50 which is used in thecircuit to delay the change in potential of a base 52 of a transistor54. The capacitor 50 preferably is of the commercially availabletantalum electrolytic type having a capacitance of approximately 80 mfd.These capacitors have a lower leakage than the more commonly knownaluminum foil electrolytics. When capacitors of the type indicated areemployed, higher charging currents than outlined in application SerialNumber 687,635, now Patent 2,929,980, concurrently filed herewith may beemployed. The relatively high capacity and low leakage of thiscapacitor, if desired, may be used to justify the omission of thetempera- .ture compensation means which is clearly shown in theapplication. It is clearly apparent that if extremely accurate time ratedelays are desired the temperature com- .pensation may be included inthe circuit shown in the present application.

In the circuit shown in FIG. 2, a transistor 56 controls the constantcurrent charging of the timing capacitor 50 during acceleration of themotor 10. Before the starting switch, not shown, is closed, a closedswitch 58 will provide a discharge path for capacitor 50. During motoroperation the switch 58 is open and the motor will accelerate when thestarter switch is initially actuated or the slider 42 on potentiometer38 is moved upwardly to increase the speed setting of the motor. Thischange of the slider 42 position will produce a positive voltage rise ofbase 60 relative to collector 62 of transistor 56. The reference voltagesignal source in turn provides a voltage signal from the slider 42 tothe collector 66 of transistor 68. When the slider 42 is moved upwardlyto increase the motor speed, the collector 66 will become positive tothe base 70 and the transistor acts as a diode to pass current from thecollector to base with a low voltage drop characteristic of reverseconduction through a transistor. This reverse conduction of transistor68 will cause the base 60 of transistor 56 to become positive relativeto the collector 62 and cause the collector 62 to pass a current whichis almost exactly equal to the current applied to the emitter 72regardless of the collector 62 to base 60 voltage to charge thecapacitor 50 at a constant rate. The value of the current to the emitter72, which in turn will determine the rate of charge of capacitor 50, isadjustable by means of the variable resistance of potentiometer 88. Inorder to explain the charging path for the capacitor 50 duringacceleration it may be said that the current flow from one plate of thecapacitor passes through the slider 42 and from the collector 66 to base70 and then through the secondary winding 76, diode 80 and potentiometer88 to the emitter 72 and collector 62 to the other plate of capacitor50-. In this connection it is to be noted that the current fromtransformer winding 76 provides the charging current and appears as aconstant current through emitter 72.

Thus it will be seen that the potentiometer 38 serves as a source ofvoltage for controlling the charging capacitor 50 when the slider 42 ismoved upwardly to cause the motor to accelerate. When the slider ismoved downwardly, the reference signal supplied to collector 62 is morepositive than the signal supplied by slider 42. When the collector 62 ismore positive than base 60, the transistor 56 acts as a diode andconducts current in the reverse direction with the characteristic lowvoltage drop.

The transistor 68 is connected in a symmetrically opposite fashion totransistor 60. When the collector 62 is more positive than the base 60,the capacitor discharges through the circuit causing the base 70 oftransistor 68 to become positive relative to the collector 66 which hadits potential decreased when the slider 42 was moved downwardly. Thiswill cause an increase in the current through collector 66. Thedischarging current for capacitor 50 which flows through base 60 ispassed through the emitter 74 through a circuit which includes thesecondary winding 76 of transformer 78, the diode 80, the lead 82 andthe deceleration potentiometer 84. This circuit will permit the chargeon the capacitor 50 to be reduced in a controlled rate as dictated bythe resistance value of the potentiometer 84.

The transformer 78 which is energized through its primary winding 86from a suitable alternating source not shown, provides a substantiallyconstant current at a low D.C. voltage to the emitters 72 and 74 throughthe diode 80. The value of this emitter current can be varied bypotentiometers 84 and 88 to provide an arrangement whereby the time rateaction during deceleration or acceleration of the motor 10 can be variedselectively. During acceleration, that is, when the time rate capacitor50 is charging, the base 52 is rendered increasingly positive relativeto the collector 90 and the transistor 54 decreases its conduction. Thisaction of transistor 54 is lWCll known and is a consequence of itsconnection in con- ',ventional emitter follower arrangement whereby thedecreasing current drawn by the resistor 92 is provided by decrease ofcollector conduction without appreciable cur- .rent flow from capacitor50. When the capacitor 50 is discharging, during deceleration, the base52 is rendered l-increasingly negative relative to collector 90 and the',conduction of transistor 54 is increased. The time rate "'action ofcapacitor 50 in either charging or discharging direction terminatessharply as soon as the voltage of the timing capacitor 50 equals thepotential at slider 42. When this occurs, the time rate circuit showncontinues {to conduct only the minute value of current to base 52 tomaintain the steady state output voltage regulation. Further, it isclearly apparent that the transistor 54 migh be connected to a secondtransistor in a conventional cathode emitter follower amplifierarrangement to further amplify the delay time rate signal change of theslider 42. The motor speed regulating controller 16 as shown may beeither voltage or current sensitive device such as shown in Patent2,902,634 or Patent 2,786,975 mentioned supra and the incorporation ofthe time delay circuit 20 according to the present invention will beclearly apparent and may be accomplished as follows: in Patent 2,902,634a reference voltage source comprising a potentiometer resistance isindicated by a numeral 14. An error voltage signal proportional to thespeed of the motor to be regulated is provided by a potentiometer whichis indicated by a numeral 15. Connected in circuit between thepotentiometers l4 and 15 is a time rate controller which delays anychange in the reference voltage signal from potentiometer 14 to acapacitor 18. The capacitor thus acts as an artificial reference voltagesignal and reflects, after a predetermined interval, changes which havebeen made in the setting of potentiometer 14. The voltage potentialsacross the capacitor 18 and the potentiometer 15 are impressed across anerror detector which is shown as a bias control winding 17 of a magneticamplifier. The winding 17 is connected in series wtih the capacitor 18and the potentiometer 15.

When the time rate controller 20 according to the present invention isincluded in the circuit shown in Patent 2,902,634, it replaces the timerate controller as disclosed in the patent. The slider 42 corresponds tothe slider on potentiometer 14 and the capacitor 50 corresponds to thecapacitor 18 of the patent. In the circuit shown in FIG. 2, thetransistor 54 acts as a current amplifier and amplifies the voltagechanges appearing across capacitor 50 to cause the voltage changes toappear as amplified current changes across leads .24 and 26. Thus whenthe circuit shown in FIG. 2 is connected to the controller shown inPatent 2,902,634, the emitter 64, the

collector 90 will be connected in a series circuit which includes thebias winding 17 and the potentiometer of the patent.

The capacitor 94 is included to filter the undesirable rectifier ripplevoltage in the circuit which includes the transformer winding 76 and thediode 80. From the above it is apparent that the transistors 56 and 68operate under constant emitter currents which are supplied from winding76 and controlled by potentiometers 88 and 84. When the transistors areoperated with constant emitter currents, the small changes in voltagesignals in the bases thereof will be amplified and appear as constantcurrent to the collectors of the respective transistors which collectorcurrent is independent of the potential between the collectors and thebases. This constant current is used to charge or discharge thecapacitor 50 at a constant rate which rate terminates sharply when thepotential between the collectors and the bases becomes equal. Thischaracteristic of the transistor is utilized to an advantage in theinstant application to provide a linear charging rate for the time ratecapacitor so that .the changes in speed of the motor will be constantuntil the desired speed setting of the motor is accomplished.

'In the description and drawings of the circuit it will be noted thatcertain conventional elements such as circuit limiting resistances,by-pass surge capacitors, etc., have been omitted to simplify theexplanation of the circuit and its operation. These elements are wellknown to those skilled in the art and the value of such components anddescriptions will be obvious.

While certain preferred embodiments of the invention have beenspecifically disclosed, it is understood that the invention is notlimited thereto, as many variations will be readily apparent to thoseskilled in theart and the invention is to be given its broadest possibleinterpretation within the following claims.

What is claimed is:

1. An adjustable reference voltage unit having predetermined rates ofvoltage change, comprising; an adjust-able constant voltage sourceproviding an input voltage signal for the unit, a capacitor providing anoutput reference voltage signal for the unit, a pair of transistorshaving common base connected electrodes, and each having an emitter anda collector electrode, a separate direct current source connectedbetween the emitter electrodes and bases of said transistors to providethe emitter electrodes with constant currents, and means connecting theinput voltage signal source and the output signal source respectively tothe collector eletcrodes of the transistors in a circuit for chargingand discharging the capacitor at a rate determined by the current flowthrough the emitters in response to changes in the input voltagesign-a1.

2. An adjustable reference voltage unit having predetermined rates ofvoltage change comprising; an adjustable voltage reference sourceproviding an input for the unit, a capacitor for providing a timedoutput reference voltage signal, a pair of common base connectedtransistors each having an emitter and base with the bases thereofconnected together, a separate direct current source connected betweenthe bases and emitters of the transistors to provide each of theemitters with an adjustable constant current, each of said transistorsalso having a collector electrode with the collector of one of thetransistors connected to the voltage reference source and the collectorof the other transistor connected to the capacitor to transmit changesin voltage potential of the reference source through the transistors tothe capacitor at a rate determined by the current flow through saidemitters.

3. The combination as recited in claim 2 wherein the capacitor isconnected to the base of an additional emitterfollower connectedtransistor which is arranged to act as a current amplifier in responseto changes in the output reference voltage signal.

4. In a time delay circuit, the combination comprising; a referencevoltage source providing an input voltage signal for the circuit, acapacitor providing an output voltage signal for the circuit, at leastone comomn base connected transistor having an emitter, base andcollector with the base connected to have the input signal impressedthereon and the collector connected to have the output signal impressedthereon, a separate floating D.C. source connected in circuit with thebase and emitter for providing the emitter with an adjustable constantcurrent whereby an increase in potential in the input signal istransmitted to the capacitor by the transistor at a rate determined bythe emitter current flow.

5. In a time delay circuit, the combination comprising; a referencevoltage source providing an input voltage reference signal, a timingcapacitor providing an output voltage signal, a common base connectedtransistor having; a base connected to have the input voltage signal ofthe reference source impressed thereon and a collector electrodeconnected to the capacitor, said transistor also having an emitter, aseparate floating source connected be tween the emitter and base of thetransistor arranged to provide the emitter electrode with a constantcurrent whereby an increase in potential of the reference signal istransmitted to the capacitor through the transistor at a rate determinedby the current flow through the emitter.

6. In a time delay circuit, the combination comprising; a referencevoltage source providing an input signal for the circiut, a capacitorproviding an output voltage signal for the circuit, a pair of commonbase connected transistors each having an emitter, a base and acollector, a separate floating D.C. source connected in circuit with theemitters and the bases of the transistors to provide the emitters ofsaid transistors with a constant current, and circuit means connectingthe input signal source, the capacitor, the bases and the collectors ofsaid transistors in a circuit so any algebraic differences in potentialbetween the input and output signals appears between the bases andcollectors of the transistors for controlling the conduction of thetransistors and changing the output voltage signal at a rate determinedby the current flow through the emitters of the transistors in responseto said algebraic difference.

7. In a time delay circuit, the combination comprising; a referencevoltage source providing an input reference voltage signal for thecircuit, a capacitor providing an output voltage signal for the circuit,at least one common base connected transistor having an emitterelectrode, a base electrode and a collector electrode with the collectorelectrode connected to have the input voltage signal impressed thereonand the base electrode connected to have the voltage signal of thecapacitor impressed thereon, and a separate floating source of DC.current connected between the base and emitter electrodes arranged toprovide the emitter electrode with a constant DC. current whereby adecrease in potential of the input reference signal is transmitted tothe capacitor through the transistor at a rate determined by the currentflow through the emitter.

No references cited.

1. AN ADJUSTABLE REFERENCE VOLTAGE UNIT HAVING PREDETERMINED RATES OFVOLTAGE CHANGE, COMPRISING; AN ADJUSTABLE CONSTANT VOLTAGE SOURCEPROVIDING AN INPUT VOLTAGE SIGNAL FOR THE UNIT, A CAPACITOR PROVIDING ANOUTPUT REFERENCE VOLTAGE SIGNAL FOR THE UNIT, A PAIR OF TRANSISTORSHAVING COMMON BASE CONNECTED ELECTRODES, AND EACH HAVING AN EMITTER ANDA COLLECTOR ELECTRODE, A SEPARATE DIRECT CURRENT SOURCE CONNECTEDBETWEEN THE EMITTER ELECTRODES AND BASES OF SAID TRANSISTORS TO PROVIDETHE EMITTER ELECTRODES WITH CONSTANT CURRENTS, AND MEANS CONNECTING THEINPUT VOLTAGE SIGNAL SOURCE AND THE OUTPUT SIGNAL SOURCE RESPECTIVELY TOTHE COLLECTOR ELECTRODES OF THE TRANSISTORS IN A CIRCUIT FOR CHARGINGAND DISCHARGING THE CAPACITOR AT A RATE DETERMINED BY THE